Electrical Discharge in Helium and Neon. 107 
_ 4. Special attention was paid to the lag, the purity of the 
gas, and the exclusion of mercury vapour. 
_ 5. The cathode fall with aluminium electrodes which have 
‘been well “run” is at most 164 volts for helium and 170 volts for 
neon. Consequently it does not appear to be. equal to the 
‘minimum spark potential. 
6. With a cathode of sodium potassium alloy in neon, the 
minimum spark potential is near to and not greater than 145 volts, 
and the cathode fall is 85 volts. 
_ 7. The cathode fall in neon with cathodes of copper, carbon, 
magnesium and calcium is approximately 221, 217, 150, and 150 
volts respectively. 
8. Four abnormal and alternative forms of discharge were 
observed. 
(a) Corresponding to a state of very high resistance in the 
gas under examination. 
(b) A variation of the above corresponding to a transition 
stage between it and the normal discharge. 
(c) An intermittent discharge, the frequency of which 
could be controlled. 
(d) Corresponding to the discharge from a Wehnelt 
eathode. 
9. Experiments were made on the fatigue of the electrodes 
which was found to be considerable, and of two kinds. Firstly a 
true fatigue, and secondly a reluctance to allow the current to 
start for a second time when one discharge had already passed. 
10. Measurements were made on the efficiency of the light 
from the negative glow. This was found to be less than was 
expected. 
11. Peculiar physiological effects were observed, correspond- 
ing to arc blindness produced by light of very feeble intensity. 
